The Fermi paradox: where is everybody?

Scene · reconstructed from the paperworkPicture it. Los Alamos, very probably the summer of 1950. Four physicists are walking to lunch: Enrico Fermi, Emil Konopinski, Edward Teller and Herbert York. That much comes from a Los Alamos report that collected the three survivors' own accounts[jones-1985], gathered some thirty-five years after the fact. The file doesn't say what the weather was, or which table they took.

What it does say is how the conversation got there. According to the recollections in that report, the talk on the walk had turned to flying saucers, and to a joke going around about saucers stealing New York's rubbish bins. Then, at the table, in Konopinski's words, Fermi surprised us with the question "but where is everybody?"[jones-1985]

Teller and York both recalled that everyone understood at once what he meant: not the people in the canteen, but extraterrestrials[jones-1985]. York remembered Fermi going on to sketch possible answers that same day: that interstellar flight is impossible, or not worth the effort, or that civilisations do not last long enough to manage it. The three men disagree on the exact wording and on what came next. They do not disagree on the question.

I like that this is where it starts. Not in an observatory, not in a paper, but over lunch, after a joke. Fermi never published on it. The report's own summary is careful: Fermi did ask the question[jones-1985], and issues still debated today were part of the discussion.

What happened to the question after lunch is a story of other people's paper.

For a decade the question stayed a lunch-table remark. The first document in the trail is not about Fermi at all. In November 1961 Frank Drake wrote a seven-term equation as the agenda for the first SETI meeting at Green Bank[seti-drake], a way to organise what you would need to know to estimate how many communicating civilisations the galaxy holds. At the time, the SETI Institute notes, only the first term, the rate of star formation, was well known.

The next step turned a question into an argument. In 1975 Michael Hart published a paper in a Royal Astronomical Society journal arguing that a technological civilisation could fill the galaxy in a few million years[hart-1975], so the absence of visitors here means there are no extraterrestrials. I have to be honest about this one: the scan available has no text layer, so the file cites Hart's argument as it is summarised by Jones[jones-1985] and by Gray[gray-2015], not in Hart's own words.

Ten years later Eric Jones at Los Alamos went back to the source. His report, LA-10311-MS, gathered the accounts of Konopinski, Teller and York and dated the lunch, very probably, to the summer of 1950[jones-1985]. It is the closest thing the case has to a primary record, and it is a record of memories.

Then come the critics. In 2015 Robert Gray argued in Astrobiology that the paradox appears to originate in Hart's argument, not Fermi's question[gray-2015], and noted that it had once been cited in Congress as a reason to end NASA's SETI programme. In 2018 Sandberg, Drexler and Ord posted a preprint that replaced single best guesses in the Drake equation with realistic ranges of uncertainty, and found a substantial chance that we are alone[sandberg-2018].

And the newest page in the trail is the plainest. NASA's own explainer names the Fermi paradox, says exoplanet surveys have filled in a few Drake terms but most remain blank, and states: so far, we have no evidence of life beyond Earth[nasa-alone].

So the paper trail is odd. It runs from a question, through an argument, to an argument about whether there was ever an argument.

The bend in this story is not a document that changed the facts. It is a change in what people think the facts mean.

For years the silence was read as a puzzle demanding a solution. Hart's version is the sharpest: if travel is feasible and the galaxy is old, their absence here means there are none[hart-1975]. York's recollection has Fermi himself floating gentler answers, that the trip is impossible, not worth it, or that civilisations do not last, as recorded in the Los Alamos report[jones-1985]. None of these has been tested, because the evidence that would decide between them is exactly what is missing.

The turn comes when critics question the frame. Gray points out that Fermi never published on the topic and that the claim that absent visitors means no extraterrestrials was first published by Hart[gray-2015]. It is, he argues, neither Fermi's nor a paradox. Sandberg, Drexler and Ord go further. Plug point estimates into the Drake equation and you get a crowded galaxy and a puzzling silence. Give each uncertain term its realistic spread, many orders of magnitude, and an empty sky is unsurprising[sandberg-2018]. On that reading no exotic explanation is needed.

That is the fair other side, and it is a strong one. It does not say we are alone. It says the silence is not evidence of anything strange.

Here is where the file lands. The checkable claim is narrow: no search has found other civilisations, and NASA says there is no evidence of life beyond Earth[nasa-alone]. No explanation for that is accepted, and none is ruled out. Our Finding is Unexplained, and it stays there, held between those who think there is a mystery and those who think there never was one.

What would move it is the part the documents cannot supply.

I keep coming back to how little the record actually holds. A lunch, remembered decades later. An equation written as a meeting agenda. Arguments built on terms nobody can yet measure.

What the documents do not settle:

• How many Drake terms can ever be measured rather than guessed. NASA says exoplanet discoveries have filled in only a few; most remain blank[nasa-alone]. The equation, as the SETI Institute frames it, organises the unknowns[seti-drake]. It does not measure them.
• Whether the paradox is real or a modelling artefact. Sandberg, Drexler and Ord[sandberg-2018] and Gray[gray-2015] say the latter. Not everyone agrees, and the 2018 paper is a preprint; the file has not confirmed whether it has since appeared in a journal.
• What Fermi actually said. The three accounts in the Los Alamos report[jones-1985] differ on wording and on what followed. The original report at OSTI could not be opened when checked; the file relies on a transcription.
• Hart's own wording. The 1975 paper[hart-1975] is cited through others' summaries because the scan has no text layer.

And what the record does not prove, either way. An absence of evidence after a limited search is not proof of absence. A blank equation is not proof of a crowded sky.

The documents and the timeline are below. They begin with a question asked over lunch, and that question is still the most solid thing in the drawer.